Your sibling has some good links, but a decent way to think about it is, from hard to easy:

* does it have an LLVM backend?

* is it listed on the forge page?

* is it listed as having std support?

The farther you go down this list, the simpler it gets to use Rust for it.

Latest work has been on ARM boards and a ton of work on AVR, which brings 8/16 but support.